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Igor Cristino Silva Cruz/CC BY-SA 4.0

Many of us have our own little rituals before going to bed. Some of us use skincare products, drink a warm glass of milk, or even read a book before we fall asleep. Certain species of the reef-dwelling parrotfish have a strange (and rather icky-sounding) bedtime habit, though: They blow out a large bubble of their own mucus and sleep inside it.

Special glands in these fishes’ gills secrete mucus, forming a cocoon that covers their bodies. For a long time, marine scientists weren’t sure exactly why a number of parrotfish and wrasse¬†species could do this. They had many theories, though, including the cocoon serving as a shield against dust or sunlight, an early warning system, or protection against moray eels and other predators.

However, research has revealed the likeliest reason behind this nightly habit: Mucus cocoons keep these fishes safe from isopods, small crustaceans that feast on their blood. Think of it as the fishes’ version of a mosquito net, albeit for the aquatic equivalent of lice. Experiments in a controlled environment showed that isopods attacked only about 10 percent of “protected” fishes, as opposed to all unprotected fishes.

Creating a cocoon requires less than an hour of the parrotfish’s time, and about 2.5 percent of its energy. Still, it’s a relatively small price to pay for a decent night’s sleep.


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References

  • http://dx.doi.org/10.1098/rsbl.2010.0916
  • https://ocean.si.edu/ocean-life/fish/parrotfish-mucus-cocoon
  • https://www.discovermagazine.com/planet-earth/parrotfish-sleep-in-a-mosquito-net-made-of-mucus
  • https://www.nationalgeographic.com/animals/fish/group/parrotfish/
  • https://www.wired.com/2010/11/sleeping-fish-mucous/

Author: Mikael Angelo Francisco

Bitten by the science writing bug, Mikael has years of writing and editorial experience under his belt. As the editor-in-chief of FlipScience, Mikael has sworn to help make science more fun and interesting for geeky readers and casual audiences alike.